This invention relates generally to lubrication systems and, more particularly, to emergency oil supply systems for gas turbine engines.
Typically, the high pressure and low pressure shafts of a gas turbine engine are supported by three main bearings each of which is cooled and lubricated by a constant flow of oil from a main supply system. Generally, oil is gravity fed from a main supply tank to the supply pump which then provides oil under pressure through a filter to the bearings. The oil which is sprayed on the bearings collects in sumps below and gravity drains into scavenge pumps which return the oil to the main supply tank.
Since the main oil pump is gravity fed from the oil tank, the oil supply to the pump can be disrupted to starve the pump whenever a maneuver of the aircraft causes a deviation of the engine from its normal upright position. For example, during inverted flight conditions, all of the oil flows to the ceiling of the oil tank and the main oil pump will supply air only. Another maneuver which disrupts the normal gravity feed procedure is when the aircraft is operating in a negative gravity condition. Again, the main lube pump will supply only air. Failure of the main lube supply pump or other components of the supply system can also disrupt the flow of oil to the bearings.
Some bearing applications are capable of withstanding such temporary oil interruptions without resultant overheating and failure. However, there are other bearings which are exposed to more extreme operating conditions and which cannot meet the requirements of withstanding such unavoidable lube oil interruptions. One of the parameters which relates to a bearing's ability to withstand short periods of dry operation is its so-called "DN value," which represents the bore size and associated shaft speed. For example, a bearing for a high-speed core rotor will have a higher DN value and will be less capable of running dry than will a low pressure turbine shaft which necessarily has a lower DN value. Another factor which may affect this ability is the heat transfer characteristics of the housing which surrounds the bearing. For example, while a housing made of titanium material is preferable for weight purposes, the poor heat transfer characteristics make is less desirable from the standpoint of retaining the bearing heat.
It is therefore an object of the present invention to provide a means by which a high speed core rotor shaft bearing can withstand periods of oil interruption.
Another object of the present invention is the provision in lubrication systems for supplying oil to a bearing during periods of negative-G operating conditions.
Yet another object of the present invention is the provision for augmenting a gravity feed lube oil system during periods of negative-G operating conditions and during periods in which the engine is operating in the inverted position.
Still another object of the present invention is to provide an emergency lube oil supply without significantly modifying the existing systems.
Still another object of the present invention is to provide an emergency lube oil system which is economical and effective in use.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.